In the electronics industry, circuits are formed on a variety of substrate materials. Alumina (Al.sub.2 O.sub.3) is a widely used material, and typically a panel of alumina substrate material is provided from which individual substrates are eventually cut. Using known processing methods, the substrates are limited to square or rectangular shapes cut from the substrate material. Lasers are generally used to cut the substrates using a variety of techniques. In one technique, the substrate panels are perforated prior to processing of the substrates to form hybrid circuits. At the completion of processing, the panel is snapped along the perforations to form individual substrates with the circuits formed thereon. Using this method the perforations can only penetrate a slight distance into the depth of the substrate material, such as by approximately 25%, in order to retain mechanical stability during processing. This technique is not compatible with thin substrate panels, such as 10 and 15 mil thick panels. This technique allows only for the formation of square and rectangular substrates with sharp corners. Irregular shaped substrates cannot be snapped from the rigid panel without breaking.
Another known technique is dicing with a saw. Large substrate material panels are mounted with wax onto a glass plate, or are mounted with tape to a template. Typically, a six mil diamond saw is used to dice the individual substrates, completely penetrating the substrate material. The individual circuits are held on by the wax backing and tape, and then are picked off with tweezers, or the wax is melted leaving the substrates. This technique provides square or rectangular circuits only. It is possible that some internal cutouts in the substrate may be realized using this technique, however complex irregular shapes, fragile substrates, or complex cutouts cannot be realized with this technique because the substrates will crack when mounted and de-mounted rendering this technique useless for producing irregular shaped substrates.
With either technique, only square or rectangular substrates may be formed as shown in FIG. 1. FIG. 1 shows a panel of substrate material 5 with a plurality of individual rectangular substrates 6 formed therein. The individual substrates 6 are formed by breaking the substrate material along a plurality of scribe lines 7. As shown in FIG. 1, all of the individual substrates have formed thereon the same circuit traces. A further limitation of these methods is that many masks are required in order to create hybrid circuits on the substrates needed for a product utilizing various circuit designs such as a receiver module, antenna module and the like. For example, in an circuit design employing channelized modules, many individual rectangular and square substrates are needed to implement the design. Typically, only one circuit is prepared from a mask and thus many masks are needed to produce different circuits. If a technique were developed which produced irregular shaped substrates, multiple hybrid circuits could be fabricated on one substrate thereby reducing the number of individual substrates and masks needed to implement a design. Moreover, combining multiple individual irregular shaped substrates on a single photomask will further reduce the prototype cost and production cycle time.
Another limitation of many rectangular and square substrates is the amount of Wire bonding needed to connect the individual circuits. Wiring bonding is a time consuming process which effects assembly and performance of the circuit. Variability is introduced into the circuit with each bond wire, and such variation requires that aligning (or tuning) operations be preformed. Thus it is desirable to provide a substrate capable of replacing a number of square and rectangular substrates and thus reducing cost, time, and the need for alignment operations.
Additionally, space utilization in a modular design of circuits is a concern with the use of square and rectangular substrates. Specifically, the square corners on such substrates require the use of corner reliefs around the corners in the module housing, otherwise the substrates may ride up and not fit properly. This limits how closely to one another the substrates may be placed. Accordingly it is desirable to provide a substrate that minimizes the requirement for corner reliefs. As stated above, it is critical that the substrates withstand all of the required processing. If irregular shapes are made with substrates and then taped or waxed onto a backboard for processing as done in the prior art, the protrusions and non-rectangular portions of the irregular shaped substrates are delicate and will crack during saw processing and during removal from the backboard. Secondly, if the irregular shaped substrates are scribed in the substrate material prior to processing, the known techniques require a low penetration scribe line to retain mechanical stability throughout processing. With this technique, relatively high force is required to break the substrates free from the panel. Using this technique it is not possible to pop the irregular shaped substrates from the panel without breaking the delicate irregular shapes. Thus it is desirable to provide an irregular shaped substrate and a method capable of forming the same.